True.IAT's are important... Mass Air Density means more power. Denser, cooler air means less boost but more power.
But it's also true that there's not much we can do about the IATs - and the average owner doesn't care. It is what it is. A larger intercooler won't guarantee lower IATs because of heat soak and the amount of time the air is going to be in the intercooler. Mechanically some powerful fans might help but there's simply not enough room to add them.
The factory intercooler has a lot of baffling to get the air to flow through it - the aftermarket Intercoolers don't - and you can't reuse the factory baffles on the aftermarket Intercooler as there is no where to mount them and they don't fit.
The #1 reason for an aftermarket Intercooler is the increased intake air flow through it. SXTH's Intercooler can flow better then 33% more air - and their hot and cold pipes are bigger and also increase the air flow over the stock pipes.
As long as the IATs are the same between the aftermarket and factory intercooler there is a power gain because the engine can breathe better.